Electrical connection of optoelectronic devices

ABSTRACT

A method of preparing a plurality of electrically connected organic optoelectronic devices on a substrate comprising firstly preparing a plurality of organic optoelectronic devices on a substrate, by the steps of providing a patterned layer of a first conductive material over the substrate, providing layer of organic optoelectronic material over the layer of first conductive material and providing a patterned layer of a second conductive material over the layer of organic optoelectronic material, at least partially removing regions of the organic optoelectronic material which are not covered by the patterned layer of second conductive material and secondly providing electrical connections to electrically connect at least two of the plurality of organic optoelectronic devices. The organic optoelectronic devices are suitably organic photovoltaic devices or organic electroluminescent devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application is directed to a method of electrical connectionof optoelectronic devices such as organic electroluminescent devices andorganic photovoltaic devices and to electrically connected devicesobtained according to this method.

2. Brief Description of the Prior Art

The past decade has seen an increasing amount of research into the useof organic materials in optoelectronic devices, examples of such devicesinclude organic electroluminescent devices, as disclosed in WO90/13148and organic photovoltaic devices, as disclosed in U.S. Pat. No.5,670,791. Both organic electroluminescent devices and organicphotovoltaic devices are organic diodes comprising a layer of organicmaterial between two electrodes. Organic electroluminescent devices emitlight on the passage of a current between the two electrodes. Organicelectroluminescent devices have a wide range of applications in thedisplay industry. Organic photovoltaic devices generate a currentbetween the two electrodes when light is incident upon the device.Organic photovoltaic devices are viewed as a replacement for inorganicsilicon solar cells. Advantages associated with the use of organicoptoelectronic devices include a greater flexibility in the design ofmaterials and the tailoring of device properties, improvedprocessability and lower cost.

In addition to applications in the field of displays, organicelectroluminescent devices have great potential for use in large arealighting applications such as in panel lighting, emergency lighting andadvertising. When developing organic electroluminescent devices for usein large area lighting, in addition to the problems which occur indisplay technology, the skilled person is presented with a range offurther problems, in particular how to prepare a large areaelectroluminescent light source which can be operated at highervoltages, such as at mains voltage and which can be prepared in anefficient manner.

Organic photovoltaic devices have at present been used to generatevoltages of around 1V, such low voltages have relatively few practicalapplications. It is known in the art to connect silicon basedphotovoltaic cells and dye-sensitised photovoltaic cells in series inorder to provide a greater volatge output. A simple and efficient methodfor the series connection of organic photovoltaic cells would enablehigher voltages to be generated and allow organic photovoltaic devicesto access a wider range of applications.

The present application proposes a simple and efficient method for thepreparation of a number of electrically connected optoelectronic deviceson a single substrate. The method allows access to a range ofapplications including a plurality of series connected organicelectroluminescent devices on a single substrate which can be driven athigher voltages than a single organic electroluminescent device, toarrangements of organic electroluminescent devices on a single substratewhich can be driven to provide continuous light emission using an ACpower source, to a plurality of series connected organic photovoltaicdevices on a single substrate providing a higher output voltage and soenabling more practical applications and to a plurality of organicelectroluminescent devices and organic photovoltaic devices on a singlesubstrate. The method of the present invention obviates the need forexternal electrical connections between devices, simplifying processingand enabling a number of electrically connected devices to beencapsulated in a single, hermetically sealed package.

SUMMARY OF THE INVENTION

In a first embodiment the present invention provides a method ofpreparing a plurality of electrically connected organic optoelectronicdevices on a substrate said method comprising the steps of;

-   -   a) preparing a plurality of organic optoelectronic devices        comprising;        -   i) providing a substrate,        -   ii) providing a patterned layer of a first conductive            material over said substrate,        -   iii) providing layer of organic optoelectronic material over            said layer of first conductive material and        -   iv) providing a patterned layer of a second conductive            material over said layer of organic optoelectronic material,            said patterned layer of second conductive material covering            regions of said layer of organic optoelectronic material,            said patterned layer of a second conductive material            defining a plurality of optoelectronic devices,    -   b) at least partially removing regions of said organic        optoelectronic material which are not covered by said patterned        layer of second conductive material,    -   characterised in that said method further comprises the step of    -   c) providing electrical connections to electrically connect at        least two of said plurality of organic optoelectronic devices.

Organic optoelectronic devices which may be prepared by the presentinvention include organic diodes such as organic electroluminescentdevices and organic photovoltaic devices and also organic transistors,organic photoluminescent devices, organic phosphorescent devices,organic resistors and organic capacitors. Organic electroluminescentdevices and organic photovoltaic devices are preferred classes oforganic optoelectronic devices. The substrate is preferably a single,unitary substrate at the time of carrying out the method according tothe invention. The substrate may have a composite structure, forexample, comprising layers of glass and plastic, plastic and ceramic orceramic and metal.

The first conductive material may be patterned on deposition usingadditive techniques or patterned following deposition using subtractivetechniques. Organic optoelectronic materials are organic materials withoptical and/or electronic properties, such properties includeelectroluminescence, photoluminescence, fluorescence, photoconductivityand conductivity.

The second conductive material may be patterned on deposition usingadditive techniques or patterned following deposition using subtractivetechniques. The patterned layer of second conductive material coverssome regions of the organic optoelectronic material while leaving otherregions uncovered or exposed. The patterned layer of second conductivematerial serves to define a plurality of optoelectronc devices,specifically the organic optoelectronic devices are defined by the areasof overlap of the first conductive material and the second conductivematerial. The patterned layer of second conductive material effectivelyacts as a mask, protecting the underlying layer of organicoptoelectronic material during the process for the removal of theexposed organic optoelectronic material.

Electrical connectors are deposited to provide electrical connectionsbetween organic optoelectronic devices on the substrate.

Preferred methods or selectively removing said organic optoelectronicmaterial comprise removing said organic optoelectronic material using amethod selected from dry etching, laser ablation, wet etching, scribing,abrasive blasting or adhesive lift off. Dry etching is a more preferredmethod, in particular dry etching using an oxygen plasma such as anO₂/CF₄ plasma.

In a preferred embodiment said second conductive material partiallyoverlies said first conductive material, such an arrangement enableselectrical connections to be more readily made between neighbouringdevices. Where the second conductive material only partially overliesthe first conductive material removal of the organic optoelectronicmaterial not covered by the second conductive material uncovers regionsof the first conductive material. The removal of organic optoelectronicmaterial from regions of the first conductive material enableselectrical connection to be made between the first and second conductivematerials of different organic optoelectronic devices in an efficientmanner simply by depositing the connecting material such that itoverlies the second conductive material of a first device and the firstconductive material of a second device.

The connecting material may be deposited by thermal deposition, e-beamevaporation or, where a suitable conducting material is used, byprinting techniques such as ink-jet printing or screen printing.

In order to prepare devices in which it is required that light enter orexit the device through either or both of the electrodes it is preferredthat either said first conductive material and said substrate are atleast semitransparent or said second conductive material is at leastsemitransparent. Where the first and second conductive materials areopaque light may enter or leave the device through the edge of thedevice.

Where it is desired to prepare an organic photovoltaic device it ispreferred that said layer of organic optoelectronic material comprisesat least an organic electron donor and at least an organic electronacceptor. Preferably at least one of said organic electron donor andsaid organic electron acceptor comprises a semiconductive organicpolymer.

Alternatively to prepare an organic light emitting device it ispreferred that said organic optoelectronic material comprises a lightemitting polymer.

In a preferred embodiment said method further comprises the step ofproviding a layer of hole injecting or hole transporting material oversaid patterned layer of first conductive material.

In a further embodiment said substrate comprises a plastic substrate.Suitable plastics include acrylic resins, polycarbonate resins,polyester resins, polyethylene terephthalate resins and cyclic olefinresins.

The present invention is also directed to organic optoelectronic devicesprepared according to the above method, in particular the presentinvention is directed to a plurality of electrically connected organicoptoelectronic devices on a substrate obtainable according to the methodof the present invention. Preferred optoelectronic devices includeorganic photovoltaic devices and organic electroluminescent devices.

In a further embodiment the present invention is directed to a substratecomprising both organic photovoltaic devices and organicelectroluminescent devices.

DETAILED DESCRIPTION OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of preparation of electrically connectedorganic optoelectronic devices according to the present invention.

FIG. 2 shows a method of preparing series connected organicoptoelectronic devices.

FIG. 3 shows a method of preparing a device on a single substratecomprising a combination of organic electroluminescent devices andorganic photovoltaic devices.

FIG. 4 shows a large array of series connected organic photovoltaicdevices for high voltage applications.

FIG. 5 shows a d.c. voltage converter comprising a large array of seriesconnected organic photovoltaic devices on a single substrate and a lightemitting polymer device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Methods suitable for the preparation of electrically connected organicoptoelectronic devices are described with particular reference toorganic photovoltaic devices. Clearly such methods have application inthe preparation of other electrically connected organic optoelectronicdevices such as organic electroluminescent devices, organicphotoluminescent devices, organic transistors, non-light-emissiveorganic diodes, organic capacitors and organic resistors

FIG. 1 f) shows a plurality of series connected organic photovoltaicdevices 110 on a substrate 101. Each photovoltaic device comprises anelectrode comprising a high work function conducting material suitablefor accepting positive charge carriers or holes from the device, knownas the anode 102, a layer of organic photovoltaic material capable ofconverting incident light into electricity 103 and an electrodecomprising a low work function material suitable for accepting negativecharge carriers, or electrons, from the device, known as the cathode104. Neighbouring devices are electrically connected by connectors of asuitable conducting material 105.

The mode of operation of organic photovoltaic devices will be brieflydescribed. Organic photovoltaic diodes comprise a layer of organicphotoconductive material between an anode and a cathode. Organicdistributed heterojunction devices are one particularly efficient classof organic photovoltaic devices and operate in the following manner. Theelectrodes of different work function set up an internal electric fieldacross the device. The organic layer comprises a mixture of a materialhaving a higher electron affinity and a material having a lower electronaffinity. Absorption of light by the materials of the organic layergenerates bound electron-hole pairs, termed excitons. Excitons generatedon the material of lower electron affinity dissociate by transfer of anelectron to the material of higher electron affinity, the material oflower electron affinity is sometimes referred to as the electron donoror simply donor. Excitons generated on the material of higher electronaffinity dissociate by transfer of a hole to the material of lowerelectron affinity, the material of higher electron affinity is sometimesreferred to as the electron acceptor or simply acceptor. The electronsand holes generated by dissociation of the excitons then move throughthe device, with electrons moving to the lower work function cathode andholes moving to the higher work function anode. In this way lightincident on the device generates a current which may be used in anexternal circuit.

The substrate 101 of the organic photovoltaic device should providemechanical stability to the device and act as a barrier to seal thedevice from the environment. Where it is desired that light enter orleave the device through the substrate, the substrate should betransparent or semi-transparent. Glass is widely used as a substrate dueto its excellent barrier properties and transparency. Other suitablesubstrates include ceramics, as disclosed in WO02/23579 and plasticssuch as acrylic resins, polycarbonate resins, polyester resins,polyethylene terephthalate resins and cyclic olefin resins. Plasticsubstrates may require a barrier coating to ensure that they remainimpermeable. The substrate may comprise a composite material such as theglass and plastic composite disclosed in EP0949850.

The anode 102 comprises a high work function material suitable foraccepting holes into the layer of organic photovoltaic material.Suitable anode materials typically have a work function of greater than4.3 eV and may be selected from the group comprising indium-tin oxide(ITO), tin oxide, aluminum or indium doped zinc oxide, magnesium-indiumoxide, cadmium tin-oxide, gold, silver, nickel, palladium and platinum.Conducting organic polymers such as polyaniline and polythiophene andtheir derivatives may also be used as the anode material. The anodematerial may be deposited upon the substrate using any appropriatetechnique such as sputtering, vapour deposition, printing, includingink-jet printing, screen printing and flexographic printing, orspraying. The anode material may be patterned post-deposition by asubtractive technique such as photolithography. Alternatively the anodematerial may be patterned during deposition by an additive techniquesuch as screen printing.

FIG. 1 a) shows a layer of anode material 102 overlying a substrate 101.FIG. 1 b) shows a layer of anode material 102 having been patterned by asubtractive technique overlying a substrate 101, the substrate isexposed at portions where the material forming the anode has beenremoved.

In order to improve efficiency the organic photovoltaic device mayinclude further organic layers between the anode and cathode to improvecharge extraction and transport. In particular a layer ofhole-transporting material may be situated over the anode. Thehole-transport material serves to increase charge conduction through thedevice. The preferred hole-transport material used in the art is aconductive organic polymer such as polystyrene sulfonic acid dopedpolyethylene dioxythiophene (PEDOT:PSS) as disclosed in WO98/05187,although other hole transporting materials such as doped polyaniline orTPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)[1,1′-biphenyl]-4,4′-diamine)may also be used. The layer of hole transporting material may bedeposited by any suitable technique such as vapour deposition or, wherethe hole transporting material is soluble, solution processingtechniques such as spin-coating, screen-printing or ink-jet printing maybe used.

The organic photovoltaic material 103 preferably comprises an electrondonor and electron acceptor. The electron donor and acceptor maycomprise polymers or low molecular weight compounds. The electron donorand acceptor may be present as two separate layers, as disclosed inWO99/49525, or as a blend, as disclosed in U.S. Pat. No. 5,670,791, a socalled bulk heterojunction. The electron donor and acceptor may beselected from perylene derivatives such as N,N′-diphenylglyoxaline-3, 4,9, 10-perylene tetracarboxylic acid diacidamide, fullerenes (C₆₀),fullerene derivatives and fullerene containing polymers andsemiconducting organic polymers such as polyfluorenes,polybenzothiazoles, polytriarylamines, poly(phenylenevinylenes),polyphenylenes, polythiophenes, polypyrroles, polyacetylenes,polyisonaphthalenes and polyquinolines. Preferred polymers includeMEH-PPV (poly(2-methoxy, 5-(2′-ethyl)hexyloxy-p-phenylenevinylene)),MEH-CN-PPV (poly(2,5-bis (nitrilemethyl)-1-methoxy-4-(2′-ethyl-hexyloxy)benzene-co-2,5-dialdehyde-l-methoxy4-(2′-ethylhexyloxy) benzene)) andCN-PPV cyano substituted PPV, polyalkylthiophenes, such aspoly(3-hexylthiophene), POPT poly(3(4-octylphenyl)thiophene) andpoly(3-dodecylthiophene), polyfluorenes, such aspoly(2,7-(9,9-di-n-octylfluorene),poly(2,7-(9,9-di-n-octylfluorene)-benzothiadiazole) andpoly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)).Typical device structures include a blend of N, N′-diphenylglyoxaline-3,4, 9, 10-perylene tetracarboxylic acid diacidamide andpoly(3-dodecylthiophene), a layered structure comprising a layer ofMEH-PPV and a layer of C₆₀, a blend of MEH-PPV and C₆₀, a layeredstructure comprising a layer of MEH-CN-PPV and a layer of POPT, a blendcomprising MEH-PPV and CN-PPV and a blend comprisingpoly(3-hexylthiophene) andpoly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole))

The organic photovoltaic material may be deposited by any suitabletechnique. Where the organic photovoltaic materials are insoluble vapourdeposition will be the preferred method. Where the organic photovoltaicmaterials are soluble solution processing deposition techniques will bepreferred. Suitable solution processing techniques include spin-coating,dip-coating, doctor-blade coating, spraying, screen-printing, ink-jetprinting and gravure printing. FIG. 1 c) shows a substrate 101, apatterned anode 102 and a layer of organic photovoltaic material 103which has been deposited over the substrate and anode using a coatingtechnique such as spin-coating.

The organic photovoltaic device may include a further layer of electronaccepting or hole blocking material between the layer of organicphotovoltaic material 103 and the cathode 104.

The cathode 104 comprises a layer of material of low work function.Examples of suitable materials for the cathode include Li, Na, K, Rb,Be, Mg, Ca, Sr, Ba, Yb, Sm and Al. The cathode may comprise an alloy ofsuch metals or an alloy of such metals in combination with other metals,for example the alloys MgAg and LiAl. The cathode preferably comprisesmultiple layers, for example Ca/Al or LiAl/Al. The device may furthercomprise a layer of dielectric material between the cathode and theemitting layer, such as is disclosed in WO 97/42666. In particular it ispreferred to use an alkali or alkaline earth metal fluoride as adielectric layer between the cathode and the emitting material.Preferred cathode structures include LiF/Ca/Al and BaF₂/Ca/Al. In somecases it may be desired that the cathode be transparent, for examplewhen an opaque substrate or anode is used or where it is desired thatthe whole device be transparent. Suitable transparent cathodes include acathode comprising a thin layer of highly conductive material such as Caand a thicker layer of transparent conducting material such as ITO, apreferred transparent cathode structure comprises BaF₂/Ca/Au. Thecathode is typically deposited by vapour deposition or sputtering.

FIG. 1 d) shows a substrate 101, a patterned anode 102, a layer oforganic photovoltaic material 103 and a patterned cathode 104. Thecathode is deposited over the organic photovoltaic material to form apattern, this is typically achieved by depositing the cathode materialas a vapour through a shadow mask. Alternative methods of patterning thecathode include printing and photolithography. The patterned regions ofanode and cathode material define a series of organic photovoltaicdevices, each device comprising an anode, an opposing cathode andorganic photovoltaic material situated between. FIG. 1 d) shows thecathode of each device partially overlying the anode of each device i.e.the cathode covers a large portion of the anode but is slightly offsetto the anode such that at one edge of the device the cathode overhangsthe anode and at the other edge of the device the cathode does notcompletely cover the anode. It should be noted that, being conductive,the organic photovoltaic material does provide some degree of electricalconnection between neighbouring photovoltaic devices but owing to thehigh resistance of the organic photovoltaic material this is notsufficient to provide an effective electrical connection of the devices.

In order to effectively electrically connect the organic photovoltaicdevices it is necessary to remove the organic photovoltaic material andany other organic materials which have been deposited, such as holetransporting materials, from regions which are not covered by thecathode material. The organic photovoltaic material may be removed by anetching technique or a mechanical technique. During the removal of theorganic optoelectronic material the cathode effectively acts as a mask,defining which areas are to be removed i.e. the uncovered portions oforganic optoelectronic material and also protecting the organicoptoelectronic material of the organic optoelectronic devices fromdamage.

Suitable etching techniques include wet etching wherein the exposedregions of organic photovoltaic material are subjected to etching usinga solvent in which the organic materials are soluble, for exampletoluene may be used to remove the organic photovoltaic layer andmethanol may be used to remove the PEDOT layer. Alternatively theorganic material may be removed using a more aggressive etching solutionsuch as an acidic solution, provided that this solution does not damagethe material of the cathode. The organic material may be removed usingdry etching wherein the organic material is exposed to a gaseous orplasma etching material, suitable dry etching materials include oxygenplasma.

Mechanical techniques for removing the organic photovoltaic materialinclude scribing the organic material with a sharp instrument, blastingthe organic material with fine particles of abrasive material,bombarding the organic material with ions, lifting off organic materialby contacting the organic material with a sheet of adhesive and thenlifting off the sheet or removing the organic material using laserablation.

The most efficacious methods for removal of the organic optoelectronicmaterial have been found to be dry etching and laser etching. Bothmethods allow the complete removal of exposed organic optoelectronicmaterials whilst not exposing the organic optoelectronic devices topotentially harmful solvents. A suitable dry etching method involvesexposing the organic optoelectronic devices to an RF or microwaveinduced O₂/CF₄ plasma for a period of between 30 and 360 seconds,preferably of between 60 and 240 seconds. An advantage of O₂/CF₄ plasmaetching is that it efficiently removes both the organic optoelectronicmaterial and additional organic layers which are generally included inthe devices, in particular the polythiophene derivative PEDOT:PSS whichis widely used as a hole transport material.

Laser ablation has also been found to be a suitable technique for theremoval of the organic optoelectronic material. Laser ablation involvesthe use of a pulsed laser having a pulse energy density of 0.4 to 1.2J/cm², a pulse rate of 50 to 150 Hz and a spot size of radius 2 to 20mm. The laser and the substrate comprising the organic optoelectronicdevices are moved in relation to each other such that the laser isfocussed on the areas of exposed organic optoelectronic material causingthis material to vaporise and so removing it from the substrate.

Following removal of the organic optoelectronic material from regionsbetween the devices the devices may be electrically connected by thedeposition of electrical contacts between devices. FIG. 1 f) shows aseries of organic photovoltaic devices 110 electrically connected by anumber of aluminum contacts 105. Electrical contacts may be made betweenany devices on a substrate although generally contacts are made betweenneighbouring devices. The electrical contacts may be formed bydepositing an electrically conducting material between devices.Deposition may be carried out using a shadow mask whereby a conductingmaterial such as aluminum is deposited as a vapour on specific regionsof the substrate through a patterned mask. Alternatively a suitableconductor may be printed onto the substrate by a technique such asscreen printing or ink-jet printing. Suitable conducting materials forprinting include silver resin pastes, graphite resin pastes and organicconducting materials such as PEDOT:PSS and polyaniline.

To facilitate the connection of the organic optoelectronic devices it ispreferred that the cathode only partially overlies the anode. The effectof this is that on removal of the organic optoelectronic material notcovered by the cathode a region of anode is also exposed, this can bereadily seen at feature 106 FIG. 1 f). The region of exposed anode canthen be connected to a neighbouring cathode through the deposition ofthe electrical connector 105. An advantage of this arrangement is thatin overlapping the anode, the cathode also provides that a region ofoptoelectronic material 107 remains between the cathode and thesubstrate. This region of organic optoelectronic material serves toinsulate the anode of the neighbouring device from the connector 105.

The organic optoelectronic device is provided with an encapsulationmeans which acts to seal the device from the atmosphere. Suitablemethods of encapsulation include covering the device on the cathode sidewith a metal can or glass sheet or providing an impermeable film overthe device, such as a film comprising a stack of polymer layers andinorganic layers.

The above embodiment is described with reference to an organicphotovoltaic device. The method of the present invention may also beadvantageously applied to the preparation of electrically connectedorganic electroluminescent devices. Organic electroluminescent devicescomprise, on a substrate, a high work function anode, an optional layerof hole transporting material, a layer of organic light emittingmaterial and a cathode. Suitable materials, and methods for theirdeposition and patterning, for the substrate, anode, hole transportinglayer and the cathode are as described above in relation to organicphotovoltaic devices.

Organic light emitting materials for use in organic light emittingdevices include polymeric light emitting materials, such as disclosed inBernius et al Advanced Materials, 2000, 12, 1737, low molecular weightlight emitting materials such aluminum trisquinoline, as disclosed inU.S. Pat. No. 5,294,869, light emitting dendrimers as disclosed inWO99/21935 and phosphorescent materials as disclosed in WO00/70655. Thelight emitting material may comprise a blend of a light emittingmaterial and a fluorescent dye or may comprise a layered structure of alight emitting material and a fluorescent dye. Due to theirprocessability soluble light emitting materials are preferred, inparticular soluble light-emitting polymers. Light emitting polymersinclude polyfluorene, polybenzothiazole, polytriarylamine,poly(phenylenevinylene) and polythiophene. Preferred light emittingpolymers include homopolymers and copolymers of 9,9-di-n-octylfluorene(F8), N,N-bis(phenyl)4-sec-butylphenylamine (TFB) and benzothiadiazole(BT).

In a particularly advantageous application of the method of the presentinvention the substrate comprises a flexible, impervious plasticmaterial such as an acrylic resin, a polycarbonate resin, a polyesterresin, a polyethylene terephthalate resin or a cyclic olefin resin, or alaminate comprising a plastic resin and an impervious inorganicmaterial. A device on a plastic substrate may be prepared in a so-calledroll-to-roll or web process whereby the organic materials are depositedby solution deposition techniques such as printing or spraying. Thepresent method has the advantage that, where suitable materials areselected, the electrical connectors can be deposited by theaforementioned solution processing techniques.

The method of the present invention allows access to a variety ofarrangements of electrically connected organic optoelectronic deviceswhich hitherto could only be obtained using complex multistep techniquesor through the integration of a number of separate units. The followingdescribes a number of arrangements of organic optoelectronic deviceswhich are made readily accessible by the method of the presentinvention.

The series connection of photovoltaic devices allows higher voltages tobe obtained. A typical organic photovoltaic cell has an open circuitvoltage of around 1V. Such low voltages are insufficient to power evenlow energy demanding applications such as calculators and watches. Thepresent invention provides a method whereby several organic photovoltaiccells can be connected in series on a single substrate, allowing greatervoltages to be generated. In addition the present invention has theadvantage that the connected organic photovoltaic cells lie on a singlesubstrate allowing easier integration of the unit into electronicdevices.

FIG. 2 shows a method for preparing a substrate comprising four seriesconnected organic photovoltaic cells. A substrate 201 comprising apatterned layer of ITO 202 is prepared using photolithography. The ITOis patterned such that it defines the areas of the four eventualphotovoltaic cells FIG. 2 a). A layer of hole transporting PEDOT:PSS isdeposited over the ITO by spin-coating (not shown). A layer comprising ablend of poly(3-hexylthiophene) andpoly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)) isthen spin-coated over the layer of PEDOT:PSS (not shown). Followingdeposition of the organic layers the device cathodes are deposited. Thecathodes comprise a layer of aluminum of thickness 300 nm and aredeposited by vapour deposition through a shadow mask. FIG. 2 b) showsthe pattern of the cathodes 203 deposited over the organic layers. Thecathodes are patterned such that the cathode at least partiallyoverhangs the anode. The organic layers which are not covered by thecathode are then removed by exposure to an O₂/CF₄ plasma. Metalinterconnects are deposited over the cathodes to provide electricalconnections between neighbouring devices. The pattern of theinterconnects 204 is shown in FIG. 2 c). The series connected devicesare finally encapsulated with a glass sheet placed over the cathodes ofthe devices and adhered to the substrate using a UV curing epoxy resin.

FIG. 2 d) shows a substrate 201 comprising four series connected organicphotovoltaic devices. The devices are comprised of an anode 202 and acathode 206 with layers of organic optoelectronic material between thetwo electrodes. The devices are electrically connected by connectors207. Feature 208 shows a region of anode material which has been exposedby the plasma treatment and is connected to the cathode of aneighbouring organic photovoltaic device.

Organic electroluminescent devices generally operate at voltages in theregion of 1 to 15V. For applications in domestic, commercial andindustrial lighting it is preferable that the light source is drivenfrom mains voltage, for example 240V. To drive organicelectroluminescent devices from mains voltage therefore requires the useof a transformer. The present invention provides a method for connectinga number of organic light emitting devices in series, these seriesconnected devices can be driven a higher voltages and do not require theuse of a transformer or other voltage conversion means. Series connectedorganic electroluminescent devices may be prepared by the abovedescribed method for the preparation of series connected organicphotovoltaic devices with the layer of organic photovoltaic materialbeing replaced by an organic electroluminescent material such aspoly(9,9-di-n-octylfluorene). Other arrangements of organicelectroluminescent devices may also be prepared such as series connectedorganic electroluminescent which may be driven by AC voltages.

The method of the present invention may be used to provide substratescomprising electrically connected organic photovoltaic devices andorganic electroluminescent devices. The advantages of such anarrangement are that the organic photovoltaic devices may be used todrive the organic electroluminescent devices so providing a source ofillumination or an information display which requires neither aconnection to a grid power supply nor a power source such as a battery.FIG. 3 a) shows a substrate 301 comprising a patterned layer of ITO 302acting as an anode, the anode is patterned to define four organicphotovoltaic devices around the edges of the substrate and an organicelectroluminescent device at the centre of the substrate. A layer ofhole transporting PEDOT:PSS is deposited over the ITO by spin-coating(not shown). A layer comprising a blend of poly(3-hexylthiophene) andpoly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)) isthen spin-coated over the layer of PEDOT:PSS (not shown). Followingdeposition of the organic layers the device cathodes are deposited. Thecathodes comprise a layer of aluminum of thickness 300 nm and aredeposited by vapour deposition through a shadow mask. FIG. 3 b) showsthe shape of the cathodes 303 of the organic photovoltaic devices whichare deposited through the shadow mask. The exposed organic material isthen removed by plasma etching and the organic photovoltaic devices areelectrically connected using connectors 304 having the shape shown inFIG. 3 c). In order to prepare the organic electroluminescent device alayer of PEDOT:PSS is deposited by spin-coating over the substrate. Alayer of the organic electroluminescent polymerpoly(9,9-di-n-octylfluorene) is then spin-coated over the layer ofPEDOT:PSS. A cathode comprising a 5 nm layer of LiF, a 10 nm layer of Caand a 100 nm layer of Al is deposited over through a shadow mask. FIG. 3d) shows the shape of the cathode 305 of the organic electroluminescentdevice. Exposed organic material is then removed by plasma etchingleaving the layer of PEDOT:PSS and the layer ofpoly(9,9-di-n-octylfluorene) beneath the cathode. The organicelectroluminescent device is then connected to the organic photovoltaicdevices by means of a connector 306 shown in FIG. 3 e).

FIG. 3 f) shows four organic photovoltaic devices and an organicelectroluminescent device connected in series on a single substrate 301.The devices comprise a common anode 302, layers of hole transportingmaterial and photovoltaic material in the organic photovoltaic devicesand a layer of hole transport material and a layer of organicelectroluminescent material in the organic electroluminescent device.The organic photovoltaic devices comprise cathode 303 and the organicelectroluminescent device comprises a cathode 305. The organicphotovoltaic devices are connected in series by connectors 304 and theorganic electroluminescent devices is connected to the organicphotovoltaic devices by connector 306.

FIG. 4 shows an array of series connected organic photovoltaic devices402 on a single substrate 401. The devices are electrically connected byconnectors 403. Such an array may be used to generate high voltages, inthe example shown the array of 14×14 organic photovoltaic devices, eachcapable of generating 1V, may be used to generate up to 196V. The methodof the present invention provides an efficient process for connectinglarge numbers of small organic electronic devices on a single substrate.For example using a substrate of size 150 mm² and organic photovoltaicdevices of size 9 mm² an array of 30×30 organic photovoltaic devices maybe connected in series, generating up to 900V.

Large arrays of organic photovoltaic devices have application in d.c.voltage converters such as that shown in FIG. 5. FIG. 5 shows a lightemitting polymer device 502 on a glass substrate 501 and a large arrayof series connected organic photovoltaic devices 504 on a second glasssubstrate 503 (for clarity the series connectors are not shown). Lightis emitted from the light emitting device on the application of avoltage of approximately 4-5V between the electrodes of the device. Theemitted light is incident on the organic photovoltaic devices and, asdescribed above, generates a voltage of several hundreds of volts,depending on the number of series connected devices in the array. Inthis way light may be used to convert a low voltage to a much highervoltage by coupling an organic light emitting device to an array ofseries connected organic photovoltaic devices. A d.c. voltage converterof the type described may also be prepared by providing the organiclight emitting device and the array of series connected organicphotovoltaic devices on either side of a single substrate, therebysimplifying the structure of the voltage converter.

EXAMPLE

Series Connected Organic Photovoltaic Devices

A substrate patterned with ITO as shown in FIG. 2 a) was cleaned in anultrasonic bath for ten minutes at 60° C., baked for 20 mins at 110° C.and treated with UV/Ozone for 90 s. 10 ml of an aqueous solution ofPEDOT:PSS (available from Bayer as Baytron) was spin-coated onto thesubstrate and the substrate was baked on a hotplate to remove remainingsolvent. A layer of PEDOT:PSS having a thickness of 60 nm was deposited.A solution comprising a 1:1 blend of poly(3-hexylthiophene) andpoly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)) ata concentration of 18 mg/l in toluene was spin-coated onto the layer ofPEDOT:PSS. A layer of polymer blend of thickness 80 nm was deposited.Aluminium cathodes were deposited over the organic layers through ashadow mask. An initial deposition rate of 0.1 nms⁻¹ was maintained to atotal thickness of approximately 50 nm, after which the rate wasincreased to 0.5 nms−1. A total cathode thickness of 300 nm wasobtained. FIG. 2 b) shows the pattern of the deposited cathodes.

To remove the organic material from regions not covered by the cathode,the substrate was placed in a barrel etcher and treated for threeminutes with an O₂/CF₄ plasma. The O₂/CF₄ plasma treatment was carriedout in a RF barrel etcher of dimensions 300 mm diameter, 450 mm depth,with a gas mixture of 0.5-2% CF₄ in oxygen, at a pressure of 1.5 Torrand a power of 400 W. Aluminum connectors were then deposited toelectrically connect neighbouring devices as shown in FIG. 2 d). Theconnectors were deposited through a shadow mask to a thickness of 300nm.

The substrate was annealed overnight for approximately 14 hours at 140°C. under vacuum in a glove box furnace. The substrate was encapsulatedusing a glass cover slide adhered with an epoxy resin.

The four series connected devices were bonded to a pair of electricalleads. The voltage generated by the four series connected devices wasmeasured to be 4V.

No doubt the teaching herein makes many other embodiments of, andeffective alternatives to, the present invention apparent to a personskilled in the art. The present invention is not limited to the specificembodiments described herein but encompasses modifications which wouldbe apparent to those skilled in the art and lying with the spirit andscope of the attached claims.

1. A method of preparing a plurality of electrically connected organicoptoelectronic devices on a substrate comprising the steps of: a)preparing a plurality of organic optoelectronic devices comprising; i)providing a substrate, ii) providing a patterned layer of a firstconductive material over said substrate, iii) providing a layer oforganic optoelectronic material over said layer of first conductivematerial and iv) providing a patterned layer of a second conductivematerial over said layer of organic optoelectronic material, saidpatterned layer of second conductive material covering regions of saidlayer of organic optoelectronic material, said patterned layer of secondconductive material defining a plurality of optoelectronic devices, b)at least partially removing regions of said organic optoelectronicmaterial that are not covered by said patterned layer of secondconductive material, and c) providing electrical connections toelectrically connect at least two of said plurality of organicoptoelectronic devices.
 2. A method according to claim 1 wherein saidstep of at least partially removing said organic optoelectronic materialcomprises removing said organic optoelectronic material using a methodselected from the group consisting of dry etching, laser ablation, wetetching and scribing.
 3. A method according to claim 1 wherein said stepof at least partially removing said organic optoelectronic materialcomprises removing said organic optoelectronic material using dryetching.
 4. A method according to claim 1 wherein said second conductivematerial partially overlies said first conductive material.
 5. A methodaccording to claim 1 wherein either said first conductive material andsaid substrate are at least semitransparent or said second conductivematerial is at least semitransparent.
 6. A method according to claim 1wherein said layer of organic optoelectronic material comprises at leastan organic electron donor and at least an organic electron acceptor. 7.A method according to claim 6 wherein at least one of said organicelectron donor and said organic electron acceptor comprises asemiconductive organic polymer.
 8. A method according to claim 1 whereinsaid organic optoelectronic material comprises a light emitting polymer.9. A method according to claim 1 further comprising the step ofproviding a layer of hole injecting or hole transporting material oversaid patterned layer of first conductive material.
 10. A methodaccording to claim 1 wherein said substrate comprises a plastic.
 11. Aplurality of electrically connected organic optoelectronic devices on asubstrate prepared according to the method of claim
 1. 12. A pluralityof electrically connected organic optoelectronic devices according toclaim 11 wherein said organic optoelectronic devices comprise organicphotovoltaic devices.
 13. A plurality of electrically connected organicoptoelectronic devices according to claim 11 wherein said organicoptoelectronic devices comprise organic electroluminescent devices. 14.A plurality of electrically connected organic optoelectronic devicesaccording to claim 11 wherein said organic optoelectronic devicescomprise organic photovoltaic devices and organic electroluminescentdevices.